An AlGaInP-based or AlGaInAs-based layer is to be understood as meaning a layer which comprises at least one material AlxGayIn1-x-yP or AlxGayIn1-x-yAs, where 0≦x≦1, 0≦y≦1 and x+y≦1. This material does not necessarily have to have a composition which mathematically precisely corresponds to the above formula. Rather, it may include one or more dopants and additional constituents which substantially do not change the physical properties of the material. For the sake of simplicity, however, the above formula includes only the main constituents of the crystal lattice (Al, Ga, In and P or As), even if these constituents may be partially replaced by small quantities of further substances.
In commercial semiconductor components based on AlGaInP or AlGaInAs, the front surface, i.e. that side of a semiconductor layer sequence which is remote from a growth substrate, is generally doped in such a manner as to be p-conducting. The reason for this is in particular the fact that commercial GaAs substrates of the required quality are only available as n-doped substrates, to which initially an n-doped epitaxial semiconductor structure is applied. For this reason, electrical contact regions for AlGaInP-based semiconductor layer sequences have hitherto been produced almost exclusively on p-doped layers.
In the text which follows, the term outer layer or external semiconductor layer is to be understood as meaning a semiconductor layer of a semiconductor layer sequence which is not followed by any further semiconductor layers, at least in partial regions, on one of two main surfaces. In particular, it is a semiconductor layer of an epitaxially grown semiconductor layer sequence which is not followed by any further semiconductor layers, at least in partial regions, on one side.
External n-conducting AlGaInP-based or AlGaInAs-based semiconductor layers with which electrical contact is to be made are found, for example, in thin-film light-emitting diodes. During fabrication thereof, the epitaxial semiconductor layer sequence is ended with a p-conducting layer, as is generally customary. Then, a carrier substrate is applied to the final p-conducting layer and the growth substrate is at least partially removed from the semiconductor layer, so that an n-conducting semiconductor layer, with which the growth was commenced, is exposed.
A further possible way of obtaining n-conducting external semiconductor layers with which electrical contact is to be made, if the growth is ended with a p-conducting layer, is for p-conducting layers to be removed at at least one location until part of an n-conducting layer with which contact is to be made is uncovered. In this way it is possible, for example in the case of a light-emitting diode, to produce both electrical contact regions on one side.
Furthermore, it is also conceivable to use technologies in which the first layer formed during growth of an epitaxial AlGaInP-based or AlGaInAs-based semiconductor layer sequence is a p-conducting layer, and the final layer is an n-conducting layer, so that an n-conducting semiconductor layer is on the outside from the outset.
To produce electrical contact region to an n-conducting AlGaInP-based or AlGaInAs-based semiconductor layer, it is possible to produce an electrically conductive contact to a GaP intermediate substrate, for example by means of direct wafer bonding, and for an electrical connection contact then to be applied to this electrically conductive contact (cf. for example F. A. Kish, F. M. Steranka et al., “Very high-efficiency semiconductor wafer-bonded transparent substrate (AlxGa1-x)0.5In0.5P/GaP light emitting diodes”, 1994, Appl. Phys. Lett. 64(21): 2839–2841). The technology used to produce an electrical connection contact which is applied direct to an n-conducting semiconductor layer of this nature, by contrast, is not yet sufficiently evolved. At the same time, there is an increasing demand for ways of producing electrical contact regions of this nature.